I am looking for help to resolve an intermittent P2187 diagnostic code issue (system too lean at idle bank 1) for a 2008 Mazda 5 (2.3L Touring) with ~120k miles.

The idle is not rough or unstable, there is no difficulty starting the engine, there is no fuel smell, no whistling or hissing noises from the engine bay and no apparent fuel economy issues.

I have replaced the following components and the code is still present.

• Engine air filter
• MAF
• EGR gasket
• Throttle body gasket
• Intake manifold runner control
• Upstream B1S1 O2 (air fuel ratio) sensor
• Purge solenoid.

A smoke test has been completed and no leaks have been found.

There are no apparent issues with the fuel filter, the fuel pump or the gas cap.

There are no other engine codes showing.

If the P2187 code is cancelled using an OBD2 scanner, the engine light will stay off for 20-100 miles (in town or highway driving), then come on with a P2187 code.

Does the group have any advice on how to diagnose and/or resolve this issue please?

 

There are more things to look at that can cause that DTC.

I suggest that you look at the full list

When you "clear" the code all you are doing is turning off the check engine light. Had you looked into the other areas of the ECU you would have seen that the DTC is still there and remains there until the issue cause it is resolved. This means that as you cycle the engine if the cause was not corrected the ECU will turn the check engine light back on generally posting at least the original DTC and many times additional DTCs. At this point your I/M monitors are also not in readiness emission related and looking at which section of the I/M are not ready can also help diagnosis the cause.
Don't rule out small exhaust leaks caused from a gasket leak that are not always detectable but the HO2 do monitor them. Also running a data or oscilloscope run on both Ho2 at start up and when the ECU switches to closed loop operations. I would also consider checking the function of the knock sensor values in the ECU by running a scan of it operating or by watching the load % vs timing values.


A DIY mistake. One last thing randomly replacing parts without first verifying that they were the cause or they are problematic often time can create additional issues on top of the original unresolved one.


Or find a service shop with a Certified Automotive Diagnostic Technician pay the hour fee for diagnosis that cause the issue and then you decide based on that if you have the ability to service the problem?

 

Welcome to the forum

 

Thanks to Callisto and others for advice.

I used my OBD-II to do a deeper dive into the short and long term trims and replaced the MAF sensor (which was an after-market sensor) with an OEM sensor purchased from https://oemusedautoparts1.com/m/mazda. (I am not affiliated with them but this may be a good source of OEM parts with quite fast delivery.)

The trims now look good, the DTC P2187 has gone and has not come back after several hundred miles of driving.